Color cathode ray tube with index stripes on ultra-violet-emitting phosphor layer



3358*-69@ XR 3,271,961() SR Sept. 6, 1966 H. B. LAW COLOR CATHODE RAY TUBE WITH INDEX STRIPES ON ULTRA-VIOLET-EMITTING PHOSPHOR LAYER Filed Aug. 26, 1963 51e/ff ifm/wad United States Patent O 3,271,610 COLOR CATHDE RAY TUBE WITH INDEX S T R I P E S ON ULTRA-VIOLET-EMI'ETING PHOSPHGR LAYER Harold E. Law, Princeton, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed Aug. 26, 1963, Ser. No. 364,311 S Claims. (Cl. S13- 92) This .invention relates to cathode ray tubes for producing color images and particularly to such tubes having an electron-sensitive screen which includes means for generating indexing signals for Ithe purpose of synchronizing the scan and color modulation of the electron beam with each other. Such tubes are sometimes known as feedback or sensing tubes. One such tube as disclosed by the prior art, includes a mosaic luminescent screen cornprising an array of color phosphor groups, each of which includes a plurality of different color-emitting phosphor strips disposed parallel to each other and perpendicular to the direction of the beam scan. A plurality of spacedapart ultraviolet light emitting phosphor strips are disposed on the back of, and parallel to, the color phosphor strips. The tube envelope is provided with a UV transmitting window rearwardly of the luminescent screen, whereby a UV sensitive phototube outside the cathode ray tube can pick up UV indexing signals which are generated when the electron beam scans across the spacedapart UV phosphor strips.

One proposed system utilizing a sensing-type cathode ray tube calls for the generation within the tube of a three (or more) level stepped indexing signal-waveform, for example, a signal having zero, maximum, and intermediate amplitude levels. In order to generate such a signal by use of prior art techniques, two dilferent arrays of UV phosphor indexing strips are used. One of the arrays comprises thinner deposits than the other so as to produce the intermediate amplitude level of the indexing signal. In order to obtain different amplitude levels by providing different thickness phosphor deposits, the thickness of the deposits should be accurately controlled. Such control is both diflcnlt and costly.

Furthermore, in order to generate an adequate indexing signal, a signicant percentage of the total electron beam energy is absorbed by the phosphor indexing strips. Since the strips are spaced apart, this absorption is in-termittent, thus giving rise to variable excitation of the imageproducing color phosphor strips. This variation, known as shadowing, results in an objectionable brightness pattern in the viewed image.

It is an object of this invention to provide in a color cathode ray tube of the sensing Variety a new and improved electron-sensitive screen structure having indexing signal generating means. Y It is also an object of this invention to provide a luminescent screen for a sensing-type color cathode ray tube which screen includes new and improved means for generating plural-level, stepped indexing signals.

According to the invention, an electron-sensitive screen includes indexing signal generating means disposed on the back of a mosaic of lcolor phosphor strips and comprises: (l) a layer of phosphor adjacent to the mosiac; (2) an array of opaque strip deposits which are disposed adjacent to spaced-apart portions of the phosphor layer and which prevent all of the luminescence from said portions from leaving the sceen, and (3) an array of absorptive strip deposits which are disposed adjacent to spaced-apart portions of the phosphor layer and which prevent a fraction only of the luminescence of said portions from leaving the screen. The opaque and absorptive strips are of such relative size and are so relatively positioned as to produce a signal of desired Wave shape (c g. a 3-level stepped wave) when scanned across by an electron beam.

The absorptive strips may consist of either opaque or semi-opaque deposits underneath the phosphor layer. In such case, a light reflective layer is provided between the mosaic and the absorptive strips. Alternatively the absorptive strips may consist of semi-opaque deposits on top of the phosphor layer.

In the drawing,

FIGURE 1 is a perspective view with parts broken away and interior greatly enlarged of a sensing-type color cath- 0de ray tube embodying the invention;

FIGURE 2 is an enlarged section of the luminescent screen of the tube of FIGURE l taken along the line 2--2 thereof;

FIGURE 2A is va schematic illustrating the waveform of the indexing signal produced by the screen of FIG- URE 2;

FIGURES 3 and 4 are sections of alternative screen embodiments of the invention which may be incorporated in the cathode ray tube of FIGURE l; and

FIGURES 3A and 4A are schematics illustrating the waveforms of the indexing signals produced respectively by the screens of FIGURES 3 and 4.

FIGURES l and 2 illustrate a preferred embodiment of the invention wherein a cathode ray tube 10' comprises an envelope 12 having an electron-sensitive luminescent screen 14 disposed on an internal surface thereof. An elec-tron gun 16 is disposed in the envelope 12 and adapted to project an electron beam onto the screen 14. A window 18 is provided in the envelope 12 rearwardly of the luminescent screen 14 for a purpose hereinafter described.

The luminescent screen 14 includes a mosaic layer 20 of diierent color emitting phosphor strips. The color strips may for example comprise alternate strips of redemitting, blue-emitting, green-emitting, and yellow-emitting, phosphors designated in the drawings las R, B, G, and Y respectively. The mosaic 20 is made up of a plurality of recurring color groups 21, each of which includes one earch of the R, B, G, Iand Y strips. The tube 10 is intended to be operated with the electron beam scanning the screen 14 and with the direction of scan being perpendicular to the color phosphor strips. The specific character of the color phosphor groups 21, for example, the width of the color strips, the color emission of the ycolor strips, the number of `color strips for each group, and the color order of arrangement of the strips within each group, may be chosen in accordance with known practices. For example, a mosaic of red, blue, and green phosphor strips may be used.

Superimposed on the back of the mosaic 20, i.e. facing toward the electron gun 16, may be a light reflective layer 22. If included, the light reflective layer 22 may, for example, `comprise a layer of evaporated aluminum which is disposed on the color mosaic 20 in accordance with known practices.

A continuous phosphor layer 24 is disposed adjacent to the mosaic 20. In screen embodiments such as the screen 14 which include a reective layer 22, the phosphor layer 24 is superimposed over the reflective layer 22. The phosphor layer 24 is preferably one which emits principally ultraviolet. For example, cesium-lithium activated calcium-magnesium-silicate phosphor known as P16 may be used. Other UV emitting phosphors, or a phosphor which emits visible light, may alternatively be used for the phosphor layer 24.

Disposed between the phosphor layer 24 and the lightreflective layer 22 is a lirst array of spaced-apart absorptive strip deposits 26 which rare substantially opaque to the luminescent emission of the phosphor layer 24. The absorptive strips 26 are disposed in a systematic relationship with, and parallel to, the color phosphor strips R, B, G, and Y of the mosaic 20. For example, one Vabsorptive strip 26 may be provided for every three groups 21 of the color phosphor strips. Eachabsorptive strip 26 may be disposed in overlying relationship with an R, B, G, Y, R, B, and part of a G phosphor strip. However, other width relationship, spacing relationship, and periodicity relationship of the absorptive strips 26 to the color phosphor stri-ps R, B, G, and Y of the mosaic may be provided.

Disposed on the phosphor layer 24 is a second array of spaced-apart opaque strip deposits 28 which are substantially opaque to the luminescent emission of the phosphor layer 24. Each opaque strip 28 is disposed centrally opposite one of the absorptive stripsr26. The opaque strips 28 are substantially narrower than, e.g., about two-thirds to three-fourths the width of, the absorptive strips 26.

The absorptive strips 26 consist of `a material which will absorb substantially all the luminescent emission of the solid phosphor layer 24 which impinges thereon. For example, an absorbing material such as powdered carbon or finely powdered aluminum knownY as aluminum black are satisfactory as a material for the absorptive strips 26.

The opaque strips 28 may consist of-a similar luminescence absorbing material, or they may alternatively con sist of a luminescence reflective material such as flakes of aluminum. The reason for this alternative choice of materials for the opaque strips 28 will be apparent from the description of operation of the invention hereinafter set forth.

In operation of the cathode ray tube 10, an electron beam is projected from the electron gun 16 and scanned by means (not shown) over the luminescent screen 14 so that the scanning lines are perpendicular to the direction of the R, B, G, and Y color phosphor strips, the absorptive strips 26, and the opaque strips 28. As a result of the electron beams scanning across the luminescent screen 14, the phosphor layer 24 is excited to luminescence at all times. When the electron Ibeam follows path a and impinges on the phosphor layer 24 at a point where neither the absorptive strips 26 nor the opaque strips 28 exist, a luminescent output of maximum amplitude is radiated rearwardly into the envelope 12 and through the window 18. When the electron beam follows path b and impinges ou a portion of the phosphor layer 24 which covers one of the absorptive strips 26, a luminescent output of intermediate amplitude is radiated rearwardly. Part of the luminescence is prevented from leaving the screen 14. When the electron beam follows path c and impinges on the opaque strips 28, substantially all of the luminescence from the phosphor layer 24 is absorbed or reflected depending upon the cornposition of the opaque strip 28, and thereby prevented from leaving the screen 14. Because the opaque strips 28 are intended to block all luminescent radiation from the screen 14, they may be either absorptive or reflective.

The fact that the beam along the path b produces a lower amplitude signal than the beam along path a may be explained by the presence of the reflective layer 22. When an electron beam excites the phosphor layer 24, luminescence is directed both forwardly and rearwardly. When the beam travel is along path a, the forwardly directed luminescence is reflected by the reflective layer 22 and is added to the rearwardly directed luminescence. Both the forward and the rearward luminescence leave the screen. When the beam travel is along path b, the forwardly directed luminescence is absorbed by the absorptive strips 26. The forward luminescence is thus prevented from leaving the screen. Only about one half of the useful luminescence, viz., the rearward luminescence, leaves the screen 14.

FIGURE 2A illustrates the waveform of the 3-level signal which results from a scanning of the screen 14. The signal amplitude levels a', b', and c' of FIGURE 2A are those produced respectively by an electron beam along paths a, b, and c of FIGURE 2. Amplitude level a is maximum output, b' is intermediate output and c' is zero output.

The rearwardly directed luminescent signals leaving the screen 14 are transmitted through the window 18. A suitable device 29, such as a phototube, which is sensitive to the phosphor layer 24, may be disposed opposite the window 18 to pick up the indexing signals. The signals picked up by the device 29 may be utilized according to known techniques to synchronize the color modulation and scan of the electron beam from the gun 16.

FIGURE 3 illustrates a screen 3f) embodying the invention wherein a 4-level stepped indexing signal is obtained. The screen 30 comprises a mosaic 31 which includes red-emitting, blue-emitting, and green-emitting color phosphor strips, designated in the drawing as R, B, and G respectively. As in the screen 14 of FIGURE 2, a light reflective layer 22 and a phosphor layer 24 are provided which overlie the mosaic 31. Indexing strips 32, 33, and 34 of three different degrees of opacity are provided on top of the phosphor layer 24. Each one of an array of substantially completely opaque strips 32 is flanked by a pair of'Y less opaque strips 33. Adjacent to the remote sides of the less opaque strips 33 are a pair of still less opaque strips 34. The opaque strips 32 may, for example,'comprises carbon particles. The less opaque strips 33 may, for example, comprise a material such as boron nitride mixed with a small amount of carbon. The still less opaque strips 34 may comprise boron nitride mixed with even less carbon or pure boron nitride.

When an electron beam is scanned across the screen 30 and follows path d, a maximum signal output level d (FIGURE 3A) is emitted rearwardly from the screen. When the beam strikes the screen along path e, a somewhat lower signal level e is emitted rearwardly from the screen, a small part of the luminescence being absorbed by the strips 34. When the electron beam strikes the screen along path f, an even lower signal output f is emitted rearwardly from the screen because of the even greater opacity of the indexing strips 33. When the electron beam strikes on the screen along path g, luminescence from the phosphor layer 24 is substantially completely blocked from rearwardly leaving the screen, thereby resulting in a zero signal level g. By virtue of the relative widths and opacities of the indexing strips 32, 33, and 34, a 4-level stepped indexing signal as illustrated in FIGURE 3A is produced.

FIGURE 4 illustrates a screen 35 embodying the invention wherein a 4-level stepped indexing signal is provided. The screen 35, like the screen 30, includes, in the order named, a three-color mosaic 31, a reflective layer 22, and a phosphor layer 24. An array of indexing strips 36 of a partially absorbing material such as boron nitride are disposed between the reflective `layer 22 and the phosphor layer 24. An array of partially opaque strips 38 which may consist of the same material as that of the strips 36 are disposed on top of the phosphor layer 24. Each strip 38 is disposed centrally opposite a different strip 36. Each one of an array of substantially opaque strips 40 of, for example, carbon is disposed on top of and centrally of a different one of the partially opaque strips 38.

When an electron beam impinges on the screen 35 along path h, a maximum luminescence output lz (FIG- URE 4A) is produced. When the electron beam impinges on the screen along path i, part of the forwardly directed luminescence is absorbed by a strip 36, and an output of reduced amplitude z" is produced. When the electron beam impinges on the screen along path i, part of both the forwardly directed and the rearwardly directed luminescence is absorbed by the indexing strips 36 and 38 so as to produce an even lower output signal level j. When the electron beam impinges on the screen along path k, substantially all of the luminescence is absorbed resulting in a zero level output k.

In practice, the 3-level stepped indexing signal of FIG- URE 2A has been found to be nearly as desirable, if not as desirable, as the 4-leve1 stepped signal of FIGURES 3A and 4A. Accordingly, because of the simplicity of fabricating it, the screen 14 of FIGURE 2 is preferred. This simplicity is due primarily to the fact that the screen 14 is designed so that the indexing strips 26 land 28 are substantially completely opaque to luminescence from the phosphor llayer 24. Accordingly, the construction of the strips 26 and 28 is easier than those of screens Where a signal of intermediate amplitude is obtained by adjusting the composition and/or thickness of a strip deposit.

Preferably the indexing strips 26, 28, 32, 33, 34, 36, 38, and 40 are provided from a material of relatively low density, i.e. of a relatively low atomic weight. Thus, a minimum of beam energy is absorbed by the strips and shadowing is minimized. A greater advantage is obtained when the material of the indexing strips is of lower molecular weight (less dense) then that of the phosphor layer 24. However, in cases where the material of the indexing strips is of greater density than the phosphor of the layer 24, the weight/unit area of the indexing strips required to provide opacity to :luminescence can still be less than the weight/unit area of a phosphor strip required to produce an indexing signal of useable strength.

As an example of the construction of the screen 14, the mosaic may comprise red, blue, green, and yellow emitting phosphor strips which are respectively, 20, 15, 17, and 8 mils wide and which have a weight/unit area respectively of 2.6-2.9, 1.3-1.5, 2.0-2.2, and 1.3-1.5 mg./cm.2. The retiective layer 22 may comprise evaporated aluminum which is approximately 4000 A, thick.

One index-ing strip 26 may be provided for every three color phosphor groups 21. The indexing strips 26 may comprise uniformly spaced colloidal graphite strips which are 103 mils wide, and each of which overlies an R, B, G, Y, R, and part of another G color phosphor strip. The phosphor layer 24 may comprise UV emitting lauthanum phosphate phosphor which is about 0.25 mg./cm.2. The indexing strips 28 may comprise colloidal graphite strips which are 73 mils wide, and each of which centrally overlies one of the index-ing strips 26. The indexing strips 26 and 28 may be less than 0.1 mg./cm.2 and so thin that no visibly noticeable or measurable absorption of beam energy occurs.

Application of the respective elements of the luminescent screen 14 i.e. the color mosaic strips 20, the light retiective layer 22, the phosphor layer 24, and the -indexing strips 26 and 28 may be provided by known techniques. Specifically, the carbon strips 26 and 28 may be laid down by iirst depositing a sensitized slurry containing carbon particles onto either the reecting layer 22 or the phosphor layer 24 and then insolubilizing the slurry :layer by exposing it to either actinic UV radiation or to electron bombardment.

What is claimed is:

1. A color cathode ray tube including an electronsensitive screen and electron gun means for projecting an electron beam onto said screen, said screen comprising:

(a) a mosaic of different color-emitting phosphor deposits,

(b) .a layer of phosphor adjacent to said mosaic,

(c) spaced-apart deposits which are, opaque to luminescence of said phosphor layer and which are disposed on said phosphor layer, and

(d) spaced-apart deposits which are positioned in contact with spaced areas of said phosphor layer and which absorb a portion only of the luminescence of said spaced areas.

2. A color cathode ray tube having a mosaic screen of color phosphor strips and indexing signal generating means, said indexing signal generating means comprising:

(a) a layer of phosphor overlying said mosaic,

(b) an array of opaque strip deposits which are disposed on spaced-apart portions of said phosphor layer and which prevent substantially all of the luminescence from said portions from leaving said screen, and

(c) an array of absorptive strip deposits which are disposed in contact with spaced apart areas of said phosphor layer and which prevent a part only of the luminescence of said areas from leaving said screen.

3. In a color cathode ray tube of the sensing type, a luminescence screen comprising:

(a) a mosaic of color phosphor strips,

(b) a phosphor layer disposed adjacent to said mosaic,

(c) a first array of strip deposits w-hich are disposed on iirst spaced-apart portions of said phosphor layer and which are opaque to the luminescence from said first spaced-apart portions, and

(d) a second array of strip deposits which are disposed in contact with second spaced-apart portions of said phosphor layer and which absorb a part of the luminescence from said second spaced-apart portions.

4. A cathode ray tube having electron gun means for projecting an electron beam and an electron-sensitive screen in the path of said beam, said screen comprising:

(a) a mosaic layer of color phosphor strips,

(b) a light reflecting layer on said mosaic layer,

(c) a rst array of spaced-apart carbon strips on said reflecting layer,

(d) a phosphor layer on said iirst array of carbon strips and on those portions of said reflecting layer between the strips of said first array of carbon strips, and

(e) a second array of spaced-apart carbonstrips on said phosphor layer.

5. A cathode ray tube having electron gun means for projecting an electron beam and a luminescent screen in the path of said beam, said luminescent screen comprising:

(a) a substrate (b) groups of color phosphor strips on said substrate,

(c) a light reflecting layer on the back of said color phosphor strips,

(d) a phosphor layer superimposed over said light reecting layer,

(e) an array of spaced strips of material which absorbs luminescence of the type emitted by said phosphor layer, said strips being disposed between said light reiiecting layer and said phosphor layer, and

(f) an array of spaced strips of material which is opaque to the luminescence of the type emitted by said phosphor layer, said strips being disposed on said phosphor layer.

6. A cathode ray tube including an electron-sensitive screen comprising:

(a) a mosaic layer of different color-emitting phosphors,

(b) a layer of phosphor adjacent to said mosaic layer,

(c) a reective layer between said mosaic layer and said phosphor layer which is reliective of the luminescence of said phosphor layer, and

(d) an array of spaced-apart strips of material which will absorb luminescence from said phosphor layer, said strips being disposed between said reflective layer and said phosphor layer.

7. A cathode ray tube having an electron-sensitive screen comprising:

60 (a) a plurality of groups of color phosphor strips,

(b) a light reecting layer on the back of said color phosphor strips,

(c) a lirst array of spaced-apart strips of ultraviolet absorbing material on the back of said light reflecting layer,

(d) a layer of ultraviolet-emitting phosphor over the strips of said first array of strips and over those portions of said light reflection layer between the strips of said first array of strips, and

(e) a second array of strips of ultraviolet absorbing material over said ultraviolet phosphor layer, said strips of said second array being narrower than and opposite the strips of said first array of strips.

8. A color cathode ray tube including an electron- 75 sensitive screen comprising:

3,271,610 7 8 (a) amosaic layer of color phosphor strips, phosphor layer and which are partially opaque to (b) a phosphor layer overlying said mosaic layer, lummesn from Said phosphor layer' (c) a first array of strip deposits which overlie said No references Cited.

phosphor layer and which are opaque to luminescence 5 from said phosphor layer, JAMES W. LAWRENCE, Primary Examiner.

(d) a, second array of strip deposits which overlie said A. SEGAL, ASSSMH Examiner- 

6. A CATHODE RAY TUBE INCLUDING AN ELECTRON-SENSITIVE CREEN COMPRISING: (A) A MOSAIC LAYER OF DIFFERENT COLOR-EMITTING PHOSPHORS, (B) A LAYER OF DIFFERENT ADJACENT TO SAID MOSAIC LAYER, (C) A REFLECTIVE LAYER BETWEEN SAID MOSAIC LAYER AND SAID PHOSPHOR LAYER WHICH IS REFLECTIVE OF THE LUMINESCENCE OF SAID PHOSPHOR LAYER, AND (D) AN ARRAY OF SPACED-APART STRIPS OF MATERIAL WHICH WILL ABSORB LUMINESCENCE FROM SAID PHOSPHOR LAYER, SAID STRIPS BEING DISPOSED BETWEEN SAID REFLECTIVE LAYER AND SAID PHOSPHOR LAYER. 